1. Technical Field
The invention relates generally to fifth wheel assemblies for coupling semi-trailers to tractors. More particularly, the invention relates to a carrier assembly which is mounted on the vehicle frame for movably supporting the fifth wheel supporting carriage. Even more particularly, the invention relates to such a carrier assembly which is adjustable for various width tractor frames and which facilitates positioning and replacement of the carriage on the trailer.
2. Background Information
Large highway freight trailers are usually coupled to a tractor by a fifth wheel assembly may include a top plate and a side bracket or carriage assembly having a locking device which engages the slide bracket in a selected position. The fifth wheel top plate is mounted on the carriage assembly which is movably adjustably mounted on a carrier assembly which is secured to the tractor frame.
These slide plates or carrier assemblies are usually custom made to fit a particular type of tractor due to the size of the tractor frame. For certain applications it is necessary to adjust the position of the carriage assembly on the carrier assembly in order for the locking mechanism to be compatible with the location of the trailer king pin to provide a desired weight distribution on the rear suspension of the tractor. Likewise, this position affects the turning radius that can be achieved between the tractor and trailer. This adjustment of the carrier and carriage assemblies with respect to each other and to the tractor frame is relatively complicated and expensive due to the welding and unwelding of various parts.
Carrier assemblies have various stop plates welded across the ends of the carrier to limit the position of the carriage assembly to prevent excessive movement of the carriage on the carrier assembly resulting in a dangerous turning radius and undesirable weight distribution on the tractor rear wheels. Heretofore, these stop members were welded into position and required breaking of the weld and rewelding the stop plate in a newly desired position, especially when replacing the slide plate assembly for maintenance or adaptability for use with a different trailer.
Another problem with existing fifth wheel assemblies and in particular the carrier assembly therefor, is that the racks along which the carriage assembly is movably mounted and subsequently positioned by a pair of opposed plungers or other retention mechanism, are usually single linear lengths of a rack which require replacement of the entire rack should one of the teeth become damaged. This is an expensive procedure requiring numerous welds to be broken in order to remove the rack and then rewelded along the entire length once the new rack is put in place. Likewise, the cost of the new rack is expensive for replacing only one or several broken teeth.
Still another problem with existing carrier assemblies is the unequal weight distribution of the carriage and slide plate on the carrier assembly resulting in increased maintenance problems.
Another problem with existing fifth wheel assemblies is that the spring biased plungers which secure a carriage assembly in a fixed position on a carrier assembly, may require replacement in order to match a particular width trailer frame. This is expensive and undesirable. Furthermore, over time, the biasing force of the plunger biasing springs will weaken due to wear, temperature and the harsh environment in which they are located, which could cause premature release of the plungers from the carrier rails.
Thus, the need exists for an improved carrier assembly for movably supporting a carriage assembly thereon of a tractor fifth wheel to eliminate problems with prior art carrier assemblies.